[CBJ]

A while after I installed my new Dlink DI-655 my IP phone stopped working. It did not register and I then found out that it was the router that was causing the problem. I turned off "SIP" under the firewall "Application Level Gateway (ALG) Configuration".'

The phone works again but I have no idea what ALG is and what the SIP is. Help me super computer monky

 

[binary visions]

Your router performs network address translation or NAT. It takes your single public IP and lets you run multiple computers/applications behind it using private IP addresses.

The Application Layer Gateway allows applications that ostensibly require direct internet connectivity (that is, they require a public IP address) to perform properly through NAT. For most packets, that's easy - the router swaps out the origin IP address for the public address and the packets come back where the router switches them back around. Some apps, though, like SIP and VPN can't have their packets modified or require special behavior, so the ALG actually recognizes the packets and monitors their status, changing the firewall/NAT accordingly.

SIP is the protocol your phone uses to set up and tear down its IP phone sessions. Probably the phone handles itself just fine behind a router and the routers generous attempts to play nice were screwing up the connections.

 

[CBJ]

So opening up for the SIP as this is specific for the phone is not a security problem i presume.

Again thank you for the help!

 

[binary visions]

Nope. Actually, you didn't open anything - you just told the router to stop dicking around with the SIP packets and let them go through the gateway normally.